In its years of searching for the secret of longevity, science has come up with one answer that isn't terribly appealing: Cut way back on food.

A new study offers an intriguing alternative, at least for the nematode. The tiny worms lived 20 percent to 33 percent longer - an extra four to seven days - when they ingested a type of antidepressant.

An antidepressant, that is, for humans. For worms, it seems to prevent the nervous system from recognizing when the organism has eaten, the authors reported in Nature on Thanksgiving, of all days.

The animals' bodies may be responding as if they were in a state of starvation, leading to a longer life, even though they've had plenty of food, says lead author Michael Petrascheck.

The researchers tested 88,000 chemicals. Some were toxic, but most had no effect on the three-week lifespan of the species, called C. elegans. More than 100 seemed to make the worms live longer, including one similar to drugs that affect the body's use of the neurotransmitter serotonin.

"I didn't really believe it," says Petrascheck, a biologist at Fred Hutchinson Cancer Research Center in Seattle.

So the team exposed the worms to 20 more chemicals that affect the serotonin pathway.

The drugs known as SSRIs, which enhance serotonin, had no effect. But those that block serotonin, including one called mianserin, did extend lifespan.

Both SSRIs and mianserin are antidepressants, though they work in opposite ways.

It's not clear if mianserin would promote longevity in people or be effective against age-related disease. As with the worms, however, it alters humans' perception of food intake.

One of its side effects in people: increased appetite. - Tom Avril